SoftBank has reportedly begun discussions with Deutsche Telekom about a takeover of T-Mobile US should it fail in its attempts to buy rival network operator Sprint.

The Japanese operator is pursuing a deal to buy a 70% stake in Sprint (Overland Park, KS, USA) for $20.1 billion, but faces competition from satellite TV provider Dish Network (Meridian, CO, USA), which has offered $25.5 billion for Sprint.

According to sources cited by Reuters, an alternative for SoftBank might be to acquire the 74% stake in T-Mobile US (Bellevue, WA, USA) owned by Deutsche Telekom (Bonn, Germany).

Although its primary target remains Sprint, SoftBank regards a move for T-Mobile US as a ‘plan B’ if that deal ultimately falls through, reports Reuters.

Sources apparently claim that SoftBank was in discussions with Deutsche Telekom last year and that talks between the two companies recently resumed following Dish Network’s counter-bid for Sprint.

Sprint shareholders are set to vote on SoftBank’s offer later this week, but proxy advisor Glass Lewis has said the vote should not take place until Sprint’s board has finished reviewing Dish Network’s offer.

Some analysts believe SoftBank’s talks with Deutsche Telekom are a ploy to put pressure on Sprint’s shareholders ahead of the vote, but others reckon SoftBank may have to raise its offer to see off competition from Dish Network.

Complicating the issue is the fact that both Sprint and Dish Network are locked in a takeover battle of their own for Clearwire (Bellevue, WA, USA), a mobile broadband operator controlled by Sprint.

While Sprint is keen to acquire the shares in Clearwire it does not already own, Dish Network believes an acquisition would dramatically improve its portfolio of spectrum holdings.

Nevertheless, a potential obstacle to a deal between SoftBank and Deutsche Telekom could be opposition from MetroPCS (Richardson, TX, USA), which merged with T-Mobile USA to form T-Mobile US and owns the 26% stake in the business not held by the German incumbent.

Indeed, the terms of the merger deal preclude Deutsche Telekom from selling shares in the newly listed T-Mobile US for 18 months.

According to Reuters, however, SoftBank is not troubled by this restriction a problem because regulatory approvals and the other steps needed to close a deal would likely take months.

Moreover, Deutsche Telekom was recently reported by Bloomberg to have insisted that its deal with MetroPCS allows it to sell its stake in one go to a third party.